Brake force control system for vehicles especially motor vehicles

ABSTRACT

A brake force control system for vehicles, especially for motor vehicles in which one or several electrical signals dependent on the wheel acceleration are compared with predetermined threshold values and in which the resultant electrical signals are utilized for the control of actuating elements such as solenoid valves in the brake circuit, whereby the electrical acceleration signals are weighted in a manner known as such and this weighting is adapted to be influenced or even discontinued when exceeding the threshold value and/or in dependence on the polarity of the acceleration signal.

Esslingen; Horst Grossner, Geradstetten; Hans-Jorg Florus, Goppingen, all of Germany [22] Filed: Sept. 3, 1971 [211 Appl. No.: 171,744

307/229, 307/230, 307/237, 328/127, 328/142 [51] Int. Cl....; B60t 8/12 [58] Fieldof Search 188/181 A; 235/183, 197;,

[56] References Cited v UNITED STATES PATENTS 3,514,635 5/1970 Gilbert 307/229 X United States Patent [191 v [11 3,802,747

Burckhardt et al. L Y 5 Ap 97 [5 BRAKE FORCE CONTROL SYSTEM FOR 3,532,392 10/1970 Scharlack 3021/21 BE x V C ESPECIALLY MOTOR 3,537,758 1 1/1970 Buhler et a1. 303/21 BE X I 3,548,323 12/1970 Gordon CI a1 307/230 X 3,636,332 1/1972 Nelson et al.... 307/229 X [76] Inventors: Manfred lLBurckhardt, 3,648,041 3/1972 Beatrice 307/229 X waibling n; l-lell g K h 3,608,979 9/1971 Coyle 188/181 A UX Primary E.\'aminerDuane A. Reger Assistant E.\'aminer-Stephen G. Kunin Attorney, Agent, orFirm- Craig and Antonelli 57 ABSTRACT celeration signals are weighted in a manner known as such and this weighting is adapted to be influenced or even discontinued when exceeding; the threshold value and/or in dependence on the polarity of the acceleration signal;

, 27 Claims, 6 Drawing Figures PATENTEUAPR '9 m4 SHEET 1 I]? 2 THRESHOLD SWITCH SIGNAL [I WITHOUT I :1 I ,I4f- 25,

I I I I I II I I 20 5 WITH LIMITATION MANFRED H BURCKHARDLHELLMUT KROHN IN VENTORS HORST GROSSNER ,HANS-JORG FLORUS BY m Qmnwm y ML ATTORNEYS )ATENTEBAPR 91914 $802,747

sum 2 0F 2 INVENTORS [IE 5 MANFRED H. BURCKHARDT,HEL LMUT KROHN 4 HORST GROSSNER HANS-JORG FLORUS BY 9 w ATTORNEYS BRAKEFORCE CONTROL SYSTEM FOR VEHICLES ESPECIALLY MOTOR VEHICLES The present invention relates to a brake force control system for vehicles, especially for motor vehicles, whereby one or several acceleration-dependent electrical signals are compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members, forexample, solenoid valves in the brake circuit.

Fully electronic brake force control systems of the aforementioned type derive their acceleration signals generally by differentiation of the voltage proportional to the wheel rotational speed. A conventional threshold switch is controlled by this differentiated voltage, whose signal is utilized for the decision as regards control of the actuating members in the brake circuit, for example, of electric solenoid valves. In these installations spurious error signals occur, which can be traced back, for example, to the movement of the wheel when passing over road unevennesses. These spurious signals, of course, should not enter the brake force control. In order now to filter out such spurious signals, a so-called integral time behavior is necessary before the threshold formation, i.e., an acceleration pulse which is to be effective for the brake force control system must last for a certain time in order to be able to distinguish the same from shorter spurious signals. However, it is desirable in connection therewith to permit this time behavior to become effective only prior to the threshold value formation and not, for example, generally because otherwise the course and characteristic of the control cycles can be unfavorably influenced during the brake force control.

The present invention is concerned with the task to provide a solution for the aforementioned problems. This task is solved according to the present invention with the brake force control systems described hereinabove in that the electric acceleration signals are weighted or evaluated as a function of time in a manner known as such and-that this weighting or evaluation is adapted to be influenced or even discontinued when exceeding the threshold value and/or in dependence on the polarity of the acceleration signal.

The effectiveness of the integral time behavior or transient phenomenon is limited by the construction according to the present invention, to the phase prior to the threshold value formation so that the aforementioned disadvantages cannot occur whereas spurious error signals can be effectively filtered out as before. Additionally, it is also possible with the present invention to weight or evaluate differently acceleration and deceleration signals.

The weighting or evaluation of the acceleration sig nal in dependence on time, i.e., therefore the integral time behavior can be achieved by a parallel connection of a capacitor with a resistor, which determines proportionately the magnitude of the acceleration signal and which may be arranged, for example, in a voltage divider circuit. However, the present invention prefers a solution according to which an operational amplifier of conventional construction with a capacitor and resistance in the feedback circuit serves for the timedependent weighting or evaluation of the acceleration signal.

In one solution according to the present invention a diode is connected in parallel to the condenser in the feedback branch, which limits the voltage rise to a value directly above the threshold value. It is achieved in this manner that the threshold. value signal is subjected at the beginning to the integral time behavior whereas at the end the threshold value signal proceeds practically without integral time behavior.

Another solution of the present. invention resides in that an electronic switching element is seriesconnected with the condenser in the feedback branch,

which eliminates the effectiveness of the condenser when exceeding the switching threshold. A thyristor or the like may be used for, that purpose. However, the present invention prefers as switching element a transistor controlled by a conventional threshold switch in such a manner that the transistor is blocked, i.e., becomes non-conductive when the threshold switch flips over. The integral time behavior is automatically turned off in this manner when exceeding the threshold value, i.e., no delay occurs any longer at the end of the threshold switch signal.

Another proposal of the present invention resides in that an additional time element is arranged in parallel to the time element provided in the feedback circuit and operable for a positive voltage, which additional time element is constituted by a resistance end capacity and is effective exclusively for negative voltages by means of a diode connected in series with the same. It can be achieved in this manner that acceleration and deceleration signals are weighted or evaluated differently.

' It should be expressly mentioned in that-connection that the features of the present invention described inv detail hereinabove are not mutually exclusive. Instead, these features can be combined for the application in a fully electronic-brake force control system in which the signal voltage proportional to the wheel acceleration is realized by electrical differentiation of an electrical voltage proportional to the rotational speed of the wheel. The amplifier provided thereby for the electroni differentiation may be utilized at the same time also for the influenced integral time behavior. It is particularly advantageous if, according to the present invention, the turning off or discontinuance of the integral time behavior is combined by means of a conventional electronic switching element with the differing weighting or evaluation of acceleration and deceleration byv means of an additional time element. lt is thereby additionally proposed in accordance with the present invention that for a limitation of the output voltages in both directions two oppositely connected diodes, preferably Zener diodes, are arranged in parallel to the feedback circuit.

Accordingly, it is an object of the present invention to provide a brake force control system for vehicles, especially for motor vehicles, which avoids by simple means the aforementioned shortcomings and drawbacks encountered in the prior art.

Another object of the present invention resides in a brake force control system for vehicles which permits a filtering out of error signals, yet does not unfavorably influence the control cycles during the brake force control. I

A further object of the present invention resides in a brake force control system for vehicles, especially for motor vehicles in which acceleration and deseleration signals can be weighted differently. deceleration These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of ilustration only, several embodiments in accordance with the present invention, and wherein:

FIG. 1 'is a schematic circuit diagram of an arrangement with a limit-effect in accordance with the present invention;

FIG. 2 is a schematic diagram explaining the operation of the arrangement according to FIG. 1;

FIG. 3 is a schematic circuit diagram of a modified embodiment with a turn-off effect in accordance with the present invention;

FIG. 4 is a schematic diagram explaining the operation of the arrangement according to FIG. 3;

FIG. 5 is a schematic circuit diagram of a still further modified arrangement in accordance with the present invention for the differing evaluation of acceleration and deceleration, and,

FIG. 6 is a schematic wiring diagram of a combined installation in accordance with the present invention.

Referring now to the drawing wherein like reference numerals are used through the various views to designate like parts, and more particularly to FIG. 1, the part of interest herein of an electronic brake force control installation for motor vehicles which as to the rest is of conventional construction and therefore not illustrated herein, is constructed as operational amplifier generally designated by reference numeral 10. The pulses of the wheel sensor prepared-by the electronic apparatus of conventional construction are fed to the operational amplifier 10 by way of a line 11 constituting the input thereof. The line 12, constituting the output thereof, is applied to a conventional threshold switch 28 providing an output which serves for the control of the actuating members (not shown), for example, of the solenoid valves in the brake circuit. A resistance element 13 is connected in the feedback circuit of the operational amplifier, which together with the input resistance element 14 determines the proportional amplification of the operational amplifier. A condenser element 15 is connected in parallel with the resistance element 13, which together with the latter effects the integral time behavior of the operational amplifier. A Zener diode 16 is again connected in parallel with the condenser element 15, which limits the output voltage in the line 12 to a value directly above the threshold value of the switch 28.

According to FIG. 2 the operational amplifier normally has operating characteristics represented by the full line curve 17. An integral time behavior, i.e., an integral transient phenomenon results due to the additional interconnection of the condenser 15, which modifies the characteristics represented by curve 17 so that the integral time behavior now proceeds at the beginning and at the end according to the dash and dot line curve 18. It follows therefrom that the threshold switch signal represented in the lower part of FIG. 2 proceeds according to curve 19. Even though during the beginning of the now occuring delay for the filtering of the spurious signals is necessary, the analogously resulting delay at the end represented by the distance 20 is highly undesirable. The parallel connection of the diode 16 now limits the rise of the voltage of the operational amplifier to a value 21 which lies directly above the switching threshold 22 of the switch 28. As a result thereof the characteristics of the integral time behavior now proceeds at the end according to the full line curve 23 and the threshold switch signal (see thereby the lower part of the figure) collapses already according to the full line 24. Consequently, the threshold switch signal is therefore shortened in a desired manner at the end and deviates compared to the ideal condition only by the slight value now represented by the distance 25.

According to FIG. 3 the operational amplifier 10 is connected together with the resistance elements 13 and 14 and the condenser 15 in a manner already described. A field effect transistor 26 is now connected in series with the resistance 13 and a condenser 15; the transistor 26 is thereby controlled by way of the line 27 from the threshold switch 28. This control takes place in such a manner that the transistor 26 is blocked when the threshold switch 28 flips over, i.e., the effect of the condenser 15 and therewith the integral time behavior is effectively turned off when reaching the threshold value. A resistance 29 thereby enables the discharge of the condenser 15.

' The operation of the arrangement of FIG. 3 can be seen from FIG. 4. According to this figure, at the beginning the voltage again follows the full line curve 18 conditioned by the integral time behavior, but only up to the point when the switching threshold 22 is reached. From there on the voltage follows the original characteristics 17 of the operational amplifier due to the effective disconnection of the condenser 15, i.e., it can be clearlyrecognized that now at the end of the signal, also the slight time delay according to the arrangement of FIG. 1 represented by the distance 25 in FIG. 2 is eliminated.

According to FIG, 5 the operational amplifier 10 is again connected with the resistance elements 13 and 14 as well as with the condenser element 15 in the manner described above and provides an output to the threshold switch 28. An additional time element generally designated by reference numeral 30 is now connected in the feedback branch in parallel with the resistance element 13 and the condenser 15. The additional time element 30 again consists of a resistance element 31 and of a condenser element 32. In series therewith is connected a diode 33 which lets this time element 30 become effective exclusively in the presence of negative voltages. A differing integral time behavior for positive and negative voltages, i.e., therefore for accelerations or decelerations can be achieved thereby.

FIG. 6 illustrates a combination of the arrangements described so far. The operational amplifier 10 is at first again connected with the resistance elements 13 and 14 and the condenser 15 corresponding to FIG. 1. In the input a further condenser 34 is connected in series with the resistance 14, which together with the resistance 13 represents the time constant of the differentiator. Similar to FIG. 5 an additional time element generally designated by reference numeral 30 is now connected in parallel in the feedback circuit so that positive and negative voltages are weighted or evaluated differently. A further condenser 35 effects that upon the described switching the time constant of the integral behavior is changed. The condenser 35 can be connected or disconnected as time determining element by means of the field effect transistor 26 arranged in a manner similar to FIG. 3, for example, in dependence on reaching the threshold value of the threshold switch 28 similar to FIG. 3. Additionally, two mutually oppositely series connected diodes 36 and 37 are arranged in the feedback circuit in parallel to the condensers and 35. The diodes 36 and 37 may be constructed as Zener diodes. They limit the output voltage to a predetermined value in both directions, i.e., for positive and negative voltages. The arrangement described in this figure may be utilized, in addition to its use for the electronic differentiation, simultaneously also for the influenced integral time behavior.

While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art; for example, the am plifiers, switching elements, diodes and/or circuit elements may be formed by semiconductor devices and may be combined in an integrated circuit in a known manner. Consequently, we do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim: t

I 1. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members in a brake circuit, characterized by time-dependent weighting means for evaluating electrical accelerationallsignals asa function of time including further means for influencing the time behavior of the signal during the evaluation operation in dependence on a characteristic of the acceleration signal, and threshold switch means responsive to the evaluated signal for providing the resultant electrical signal for controlling actuating members in the brake circuit.

2. A brake force control system according to claim 1, characterized in that the further means for influencing the evaluation is operable in dependence, on the polarity of the acceleration signal.

3. A brake force control system according to claim A 2, characterized in that the further means is operable todiscontinue the evaluation as a function of the polarity of the acceleration signal.

4. A brake force control system according to claim 1, characterized in that the means for evaluating the acceleration signal in dependence on time includes an operational amplifier means having a parallel arrangement ofcondenser and resistance means in its feedback circuit for integrating the electrical acceleration signal, the further means influencing the evaluated signal for permitting the signal to be subjected at the beginning portion of the signal to an integral time behavior for application to the threshold switch means and for substantially eliminating the effect of the integral time behavior of the evaluated signal at the end portions of the signal for application to the threshold switch means.

5. A brake force control system according to claim 1, wherein the time-dependent weighting means serves for integrating the acceleration signal to eliminate the effects of noise on the operation of the threshold switch means such that the threshold switch means operates with a time delay at the beginning and end portions of the evaluated signal, and the further means influences the evaluated signal to substantially eliminate the effect of the integral time behavior of the evaluated signal at the end portion thereof such that the threshold switch means operates without substantial time delay in response to the end portion of the evaluated signal.

6. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electri cal signals serve for the control of actuating members in a brake circuit, characterized by time-dependent weighting means for evaluating electrical accelerational signals as a function of time including further means for influencing this evaluation operation in dependence on a characteristic of the acceleration signal, and threshold switch means responsive to the evaluated signal for providing the resultant electrical signal for controllingactuating members in the brake circuit, the further means for influencing the evaluation being operable upon exceeding the threshold value of said threshold switch means.

7. A brake force control system according to claim 6, characterized in that the further means for influencing the evaluation is operable in dependence on the polarity of the acceleration signal. 1

8. A brake force control system according to claim 7, characterized in that the further means is operable to tum-off, in effect, the evaluation.

. 9. A brake force control system according to claimv 6, wherein the further means is operable to discontinue the evaluation when exceeding the threshold value of said threshold switch means.

10. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members in a brake circuit, characterized by time-dependent weighting means for evaluating electrical accelerational signals as a function of time including further means for influencing this evaluation operation in dependence on a characteristic of the acceleration signal, the means for evaluating the acceleration signal in dependence on time including an operational amplifier means having condenser and resistance means in its feedback circuit, the further means being arranged in the feedback circuit of the operational amplifier means.

11. A brake force control system according to claim 10, characterized in that a diode means is connected in parallel with the condenser means which limits the voltage rise to a value directly above the threshold value.

12. A' brake force control system according to claim 10, characterized in that an electronic switching means is series connected with the condenser means in the feedback circuit, which eliminates the effect of the condenser means'when exceeding the switching threshold.

13. A brake force control system according to claim 12, characterized in that a transistor means serves as switching means which is so controlled by a threshold switch means that the transistor means is rendered nonconductive when the threshold switch means flips over.

14. A brake force control system according to claim 13, characterized in that an additional time element is arranged in parallel to the time element formed by the first-mentioned condenser means which is provided in the feedback circuit and is effective forpositive voltages, said additional time element being constituted by a resistor means and a condenser means and is rendered effective exclusively for negative voltages by a diode means connected in series therewith.

15. A brake force control system according to claim 14, characterized in that two mutually oppositely connected diodes are arranged parallel to the feedback circuit for limiting the output voltages in both directions.

16. A'brake force control system according to claim 10, characterized in that an additional time element is arranged in parallel to the time element formed by the first-mentioned condenser means which is provided in the feedback circuit and-is effective for positive voltages, said additional time element being constituted by a resistor means and a condenser means and is rendered effective exclusively for negative voltages by a diode means connected in series therewith.

17. A brake force control system according to claim 16, characterized in that two mutually oppositely connected diodes are arranged parallel to the feedback circuit for limiting the output voltages in both directions.

18. A brake force control system according to claim 10, characterized in that two mutually oppositely series connected diodes are arranged parallel to the feedback circuit for limiting the output voltages in both directions.

19. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members in a brake circuit, characterized by time-dependent weighting means for evaluating electrical accelerational signals as a function of time including further means for influencing this evaluation operation in dependence on a characteristic of the acceleration signal, and threshold switch means responsive to the evaluated signal for providing the resultant electrical signal for controlling actuating members in'the brake circuit, the means for evaluating the acceleration signal in dependence on time including an operational amplifier means having an input, an output and a feedback circuit means between said input and output including a parallel resistance-capacitance network means and in that the further means are connected with said network means for changing its operability in relation to a predetermined threshold value of the threshold switching means.

20. A brake force control system according to claim 19, wherein said further meansincludes at least one diode connected in parallel with said network means.

21. A brake force control system according to claim 19, wherein said further means includes a control element operable to effectively disconnect said network means.

22. A brake force control system according to claim 21, wherein said further means includes a further network connected in parallel with said network means and including a parallel connected resistancecondenser circuit series connected with a diode.

23. A brake force control system according to claim 22, wherein said further means includes means for limiting the output voltages in both positive and negative directions.

24. A brake force control system according to claim 23, wherein said further means includes a further condenser element in parallel with said network means, said network means being series connected with a series circuit in said input including a resistor and a condenser.

25. A brake force control system according to claim 19, wherein said further means includes a further network connected in parallel with said network means and including .a parallel connected resistancecondenser circuit series connected with a diode.

26. A brake force control system according to claim 19, wherein said further means includes means for limiting the output voltages in both positive and negative directions.

27. A brake force control system according to claim 19, wherein said further means includes a further condenser element in parallel with said network means, said network means being series connected with a series circuit in said input including a resistor and a condenser. 

1. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members in a brake circuit, characterized by timedependent weighting means for evaluating electrical accelerational signals as a function of time including further means for influencing the time behavior of the signal during the evaluation operation in dependence on a characteristic of the acceleration signal, and threshold switch means responsive to the evaluated signal for providing the resultant electrical signal for controlling actuating members in the brake circuit.
 2. A brake force control system according to claim 1, characterized in that the further means for influencing the evaluation is operable in dependence on the polarity of the acceleration signal.
 3. A brake force control system according to claim 2, characterized in that the further means is operable to discontinue the evaluation as a function of the polarity of the acceleration signal.
 4. A brake force control system according to claim 1, characterized in that the means for evaluating the acceleration signal in dependence on time includes an operational amplifier means having a parallel arrangement of condenser and resistance means in its feedback circuit for integrating the electrical acceleration signal, the further means influencing the evaluated signal for permitting the signal to be subjected at the beginning portion of the signal to an integral time behavior for application to the threshold switch means and for substantially eliminating the effect of the integral time behavior of the evaluated signal at the end portions of the signal for application to the threshold switch means.
 5. A brake force control system according to claim 1, wherein the time-dependent weighting means serves for integrating the acceleration signal to eliminate the effects of noise on the operation of the threshold switch means such that the threshold switch means operates with a time delay at the beginning and end portions of the evaluated signal, and the further means influences the evaluated signal to substantially eliminate the effect of the integral time behavior of the evaluated signal at the end portion thereof such that the threshold switch means operates without substantial time delay in response to the end portion of the evaluated signal.
 6. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members in a brake circuit, characterized by time-dependent weighting means for evaluating electrical accelerational signals as a function of time including further means for influencing this evaluation operation in dependence on a characteristic of the acceleration signal, and threshold switch means responsive to the evaluated signal for providing the resultant electrical signal for controlling actuating members in the brake circuit, the further means for influencing the evaluation being operable upon exceeding the threshold value of said threshold switch means.
 7. A brake force control system according to claim 6, characterized in that the further means for influencing the evaluation is operable in dependence on the polarity of the acceleration signal.
 8. A brake force control system according To claim 7, characterized in that the further means is operable to turn-off, in effect, the evaluation.
 9. A brake force control system according to claim 6, wherein the further means is operable to discontinue the evaluation when exceeding the threshold value of said threshold switch means.
 10. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members in a brake circuit, characterized by time-dependent weighting means for evaluating electrical accelerational signals as a function of time including further means for influencing this evaluation operation in dependence on a characteristic of the acceleration signal, the means for evaluating the acceleration signal in dependence on time including an operational amplifier means having condenser and resistance means in its feedback circuit, the further means being arranged in the feedback circuit of the operational amplifier means.
 11. A brake force control system according to claim 10, characterized in that a diode means is connected in parallel with the condenser means which limits the voltage rise to a value directly above the threshold value.
 12. A brake force control system according to claim 10, characterized in that an electronic switching means is series connected with the condenser means in the feedback circuit, which eliminates the effect of the condenser means when exceeding the switching threshold.
 13. A brake force control system according to claim 12, characterized in that a transistor means serves as switching means which is so controlled by a threshold switch means that the transistor means is rendered non-conductive when the threshold switch means flips over.
 14. A brake force control system according to claim 13, characterized in that an additional time element is arranged in parallel to the time element formed by the first-mentioned condenser means which is provided in the feedback circuit and is effective for positive voltages, said additional time element being constituted by a resistor means and a condenser means and is rendered effective exclusively for negative voltages by a diode means connected in series therewith.
 15. A brake force control system according to claim 14, characterized in that two mutually oppositely connected diodes are arranged parallel to the feedback circuit for limiting the output voltages in both directions.
 16. A brake force control system according to claim 10, characterized in that an additional time element is arranged in parallel to the time element formed by the first-mentioned condenser means which is provided in the feedback circuit and is effective for positive voltages, said additional time element being constituted by a resistor means and a condenser means and is rendered effective exclusively for negative voltages by a diode means connected in series therewith.
 17. A brake force control system according to claim 16, characterized in that two mutually oppositely connected diodes are arranged parallel to the feedback circuit for limiting the output voltages in both directions.
 18. A brake force control system according to claim 10, characterized in that two mutually oppositely series connected diodes are arranged parallel to the feedback circuit for limiting the output voltages in both directions.
 19. A brake force control system for vehicles, especially for motor vehicles, whereby at least one acceleration-dependent electrical signal is compared with predetermined threshold values and the resultant electrical signals serve for the control of actuating members in a brake circuit, characterized by time-dependent weighting means for evaluating electrical accelerational signals as a function of time including further means for influencing this evaluation operation in dependence on a characteristic of the acceleration signal, and threshold switch meaNs responsive to the evaluated signal for providing the resultant electrical signal for controlling actuating members in the brake circuit, the means for evaluating the acceleration signal in dependence on time including an operational amplifier means having an input, an output and a feedback circuit means between said input and output including a parallel resistance-capacitance network means and in that the further means are connected with said network means for changing its operability in relation to a predetermined threshold value of the threshold switching means.
 20. A brake force control system according to claim 19, wherein said further means includes at least one diode connected in parallel with said network means.
 21. A brake force control system according to claim 19, wherein said further means includes a control element operable to effectively disconnect said network means.
 22. A brake force control system according to claim 21, wherein said further means includes a further network connected in parallel with said network means and including a parallel connected resistance-condenser circuit series connected with a diode.
 23. A brake force control system according to claim 22, wherein said further means includes means for limiting the output voltages in both positive and negative directions.
 24. A brake force control system according to claim 23, wherein said further means includes a further condenser element in parallel with said network means, said network means being series connected with a series circuit in said input including a resistor and a condenser.
 25. A brake force control system according to claim 19, wherein said further means includes a further network connected in parallel with said network means and including a parallel connected resistance-condenser circuit series connected with a diode.
 26. A brake force control system according to claim 19, wherein said further means includes means for limiting the output voltages in both positive and negative directions.
 27. A brake force control system according to claim 19, wherein said further means includes a further condenser element in parallel with said network means, said network means being series connected with a series circuit in said input including a resistor and a condenser. 